CROATIAN FAUNA 2007 - CRABS - RIVER CRAYFISH

River crayfish or noble crayfish (Astacus astacus Linnaeus) The river crayfish is one of the four autochthonous species of freshwater decapodous crabs from the family Astacidae that lives in Croatian rivers and lakes. Its Latin name is Astacus astacus. This species is endangered by the great quantities of waste matter in water ecosystems, the regulation of water courses and the excessive uncontrolled fishing out. It is also endangered by foreign American crayfish species that were brought to Europe and that often carry the dangerous disease – crayfish plague. The imported foreign species are resistant to crayfish plague but, on the other hand, European species, among them the river crayfish, are susceptible to it and they perish in great numbers. Besides, the American species are more aggressive than the autochthonous European species, so that in fighting for space and food they oust the latter from their habitats. As they grow fast and multiply fast it is almost impossible to subject them to control. This is why the river crayfish in Croatia is to the full protected by law (the official bulletin Narodne novine, No. 70/05 and 7/06), which means that it fishing for them and disturbing them is forbidden, and any type of scientific research of the species demands a special permission issued by the Ministry of culture. It is also protected on the European level – on account of its being thinned out it has been proclaimed a rare and endangered species and listed in the IUCN ((International Union for the Conservation of Nature and Natural Resources) Red List of Threatened Species, as well as in the Appendix III of the Bern Convention, according to which its exploitation is under the strict supervision of individual states. Crayfish of this species rarely grow bigger than 15 cm in total length. On the back side the animal is usually dark brown (olive green to black, sometimes bluish or reddish), while the lower side is green-brown coloured. The surface of the body is covered by a strong “shell”, a carapace (exoskeleton), so that crayfish cannot grow continuously. In the warmer seasons of the year they molt – lose their old shell. While they are soft they grow in length and grow a new, strong exoskeleton, usually using minerals from the old shell by eating it. The top of their head is elongated into a beaklike rostrum, and their head and thorax are fused on the breast forming the so called cephalothorax with the abdomen adjoining it. As has already been mentioned, these crabs belong to the group of decapodous crabs, which means that they have five pairs of walking legs on the belly side, of which the first pair are big and wide pincers or claws called chelipeds with warty-surfaced chelae. The chelae of the male are always bigger than the ones of the females. On the belly side of the abdomen the crabs have swimmerets that, among other things, serve the females in carrying their eggs. Both the walking legs and the swimmerets will regenerate or re-grow if they are wounded or broken off. The river crayfish mature sexually in the 2nd to 3rd year of life. The mating takes place in autumn, and the females carry eggs under the abdomen on the swimmerets for eight to nine months. When they hatch, the juvenile crabs are about 12 mm long and are very similar to the adult crabs. The crayfish of this species are nocturnal and sedentary animals, living on the bottom, they are not territorial but show aggressive forms of behaviour in cases when the space becomes a limiting factor. It is well-known that this type of a small radius of movement is characteristic of animals adapted to a habitat. If moved to a new habitat animals are more movable – the radius of their movement is from 50 to 1,000 meters in the course of a week. They live in rivers and lakes with clayey and pebbly bottoms and along the coast among the water vegetation. In Croatia they are spread in the waters of the Sava and Drava river-basin, and they have also been brought into some rivers of the Adriatic river-system territory.